The invention relates to a method for obtaining a three-dimensional map representation for a navigation system from digital, two-dimensional road map data, and to a navigation system having a three-dimensional map representation.
Digital road maps for navigation systems regularly contain two-dimensional networks of road segments and nodes connecting the road segments. The nodes are assigned geocoordinates that are defined in each case by degrees of longitude and latitude.
Published, European Patent Application EP 0 752 687 A2 discloses a three-dimensional representation from a bird""s-eye perspective for navigation systems, in the case of which the transformation of the digital road map data into the bird""s-eye perspective is optimized by use of conversion tables. The representation of the road map is performed by a perspective projection that is performed from a virtual, elevated viewpoint. The result is to produce a pseudo-3D effect that causes the plane to run together into a vanishing point.
Thus, no actual three-dimensional information is used, but the plane is still flat.
Published, European Patent Application EP 0 841 537 A2 discloses a navigation system which permits a three-dimensional map representation. Topographic features, roads and buildings are stored for this purpose as three-dimensional data. It is very expensive to set up such a database. The complete database has to be set up anew in the event of changes in road information. Conventional two-dimensional digital road maps for which there are relatively cost-effective new editions at regular intervals cannot easily be taken over.
It is accordingly an object of the invention to provide a method for obtaining a three-dimensional map representation, and a navigation system that overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which permit a three-dimensional map representation on the basis of two-dimensional, digital road map data.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for obtaining a three-dimensional map representation for a navigation system from digital, two-dimensional road map data of a road map database having a network of road segments, which includes linking the road segments to be represented with an aid of three-dimensional topological data of a separate geotopology database resulting in display data; and subsequently outputting the display data onto a display device.
The road segments of the two-dimensional road map database are linked with the aid of three-dimensional, topological data of a geotopology database and are thus incorporated into the three-dimensional structure of the topological data. The result is a true three-dimensional view that reproduces height differences in terrain. The same procedure can be adopted with all other objects, for example water bodies, forest and the like, present in the two-dimensional road map database.
An artificial elevation of objects, that is to say multiplication of the z-coordinate (height) by a factor  greater than 1, can strengthen the 3D impression. This brings out, for example, hills and valleys more strongly in visual perception.
The road map data of the two-dimensional road map database have a network of road segments with nodes or points of intersection. The nodes or points of intersection define the road segments. Each node is stored as a geodatum or geocoordinate, typically in degrees of longitude and latitude or in Cartesian coordinates. The three-dimensional topological data from the geotopology database can be determined in each case for the nodes of a road segment that is to be reproduced on the display device. In accordance with an added feature of the invention, there are the steps of connecting the road segments to one another at nodes, the nodes being assigned geocoordinates in the road map database and associated points of the three-dimensional topological data are determined for the nodes of the road segments to be output; and plotting the road segments between the associated points determined in the topological data.
If no appropriate point for a node is stored in the geotopology database, the three-dimensional topological data can be determined by interpolation. Use is made for this purpose of those three-dimensional topological data that come closest to the geocoordinate of the relevant node.
Although the road map database and the geotopology database can be accommodated on a single data medium, separate data media are preferred for the databases. In particular, the databases can be stored on different CD-ROMs which are read as required by a CD changer.
As an option, it is also possible to provide a database for textures for describing the surfaces of the topographies to be represented and for describing discrete, three-dimensional objects. In this way, it is possible, for example, to generate realistically with a suitable surface structure and color, forest and meadow sections of a landscape, or buildings. In accordance with an additional feature of the invention, there are the steps of assigning textures stored in a texture database and have a raster of the geocoordinates to go the three-dimensional topological data; and assigning objects to the three-dimensional topological data in accordance with the geocoordinates as three-dimensional geometrical bodies.
Road segments are preferably provided with boundary lines so that a road segment is firstly given a two-dimensional appearance. Subsequently, the boundary lines are distorted into a bent coarse in the region of juxtaposed road segments. This produces a particularly natural view without edges in the line of the road or at junctions, above all in the case of intense enlargement of a map section.
In a preferred embodiment, there is an alteration between a three-dimensional representation that is based on the geotopology database, and a three-dimensional representation that is based only on the two-dimensional road map data. For the latter representation, it is in each case only road map data for a field of view to be represented that are prepared with a predetermined visual range for a task. In this case, the field of view to be represented is preferably bent in a radially symmetric fashion about a virtual viewpoint by a polynomial transformation. The result is an artificial horizon. The plane to be represented is distorted like a dish.
There is preferably a switchover to the representation based only on the road map data in towns/cities or in the case of map representations for very great enlargement in which the emphasis is on the guiding information for a delimited area, for example a road intersection or a complicated juxtaposition of streets. The topographic data are frequently of lesser value in any case in the downtown area.
In accordance with another feature of the invention, there is the step of using the navigation system to continuously determine the virtual viewpoint, and displacing the field of view synchronously with the virtual viewpoint.
With the foregoing and other objects in view there is provided, in accordance with the invention, a navigation system, containing a display device; a position-determining unit; at least one storage medium for storing a road map database with two-dimensional road map data of a network of road segments; and a conversion unit receiving and converting the road segments of the two-dimensional road map database and three-dimensional topological data of a geotopology database into a three-dimensional road map representation. The conversion unit is connected to the display device for displaying the three-dimensional road map representation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for obtaining a three-dimensional map representation, and a navigation system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.